Dopaminergic deficiency and delayed visual evoked potentials in humans.

Abnormal delay in visual evoked potential (VEP) could be normalized in 9 of 14 previously untreated parkinsonian patients under the influence of levodopa/carbidopa therapy. In 6 of 11 previously untreated schizophrenic patients the VEP latency became abnormal following therapy with agents known to cause dopaminergic blockade. Besides defects in retrobulbar conduction secondary to demyelination, synaptic dysfunction due to neurotransmitter deficiency or receptor blockade must also be considered as a mechanism underlying VEP delays in humans.